The present invention relates to processes for the preparation of sodium percarbonate and more particularly to the preparation of such percarbonates substantially responding to the formula 2Na.sub.2 CO.sub.3.3H.sub.2 O.sub.2 through the use of certain hydrates of sodium carbonate and certain hydrogen peroxide strengths.
A number of processes for the preparation of sodium percarbonate have already been proposed. Among these is the procedure of Schlotterbeck described in German Patent No. 560,460. This process utilizes as feed materials 30 percent hydrogen peroxide and sodium carbonate monohydrate to provide sodium percarbonates having the formula (Na.sub.2 CO.sub.3.H.sub.2 O).sub.x.(H.sub.2 O.sub.2).sub.Y. This procedure necessitates refrigeration of the reaction mixture to maintain a temperature below 5.degree. C. The process of Kali Chemie described in Belgian Patent No. 446,540 utilizes sodium carbonate decahydrate and 40 percent hydrogen peroxide as starting materials and is carried out in the presence of magnesium salts, sodium silicate and common salt.
The Henkel process shown in French Patent No. 1.171,464 provides a sodium percarbonate containing water of crystallization and utilizes an inert organic dilution agent. The Solvay process described in French Patent No. 2,076,430 uses 20 percent hydrogen peroxide and sodium carbonate feed materials in an aqueous medium in the presence of seed particles. The reaction is carried out in a fluidized bed at a temperature in the neighborhood of 50.degree. C. with air blown into the apparatus at a temperature of at least 110.degree. C. The sodium percarbonate so obtained has the nominal formula 2Na.sub.2 CO.sub.3.3H.sub.2 O.sub.2, but its active oxygen content does not exceed 14.8 percent.
The Laporte process described in French Patent No. 2,098,191 consumes anhydrous sodium carbonate which is fluidized with air, and is carried out in the presence of 65 percent hydrogen peroxide. The required reaction time of this process is very long, It is noted that the Examples in the Laporte patent utilize overall reaction and drying times of 13 hours 10 minutes, 6 hours 45 minutes, 4 hours, and 1 hour and 20 minutes. The temperature of the fluidizing gas is maintained at 55.degree.-70.degree. C.
The foregoing processes present a number of disadvantages. The Schlotterbeck process necessitates considerable refrigeration of the reaction mixture and does not provide a sodium percarbonate without water of crystallization. The Kali Chemie process involves the use of numerous additives, while the Henkel process necessitates the use of an organic diluent and only produces hydrated sodium percarbonate. The Solvay process is awkward to carry out in practice because it requires the use of a reaction temperature considerably higher than ambient, while the Laporte process requires the reaction and drying times to be very long and by the same token requires that the anhydrous carbonate starting material be very finely divided. Moreover, the percarbonate obtained by the Laporte process cannot satisfy the actual requirements for manufacture of lixivia.